1. Field of the Invention
The present invention generally relates to a display device and a defect repairing method of the same. More particularly, the present invention relates to an active matrix display device and a defect repairing method of the same.
2. Description of the Background Art
Currently, active matrix liquid crystal display devices (LCDs) are widely used. In particular, TFT LCDs using thin film transistors (hereinafter, referred to as TFTs) as switching elements are widely used.
The TFT LCD has picture elements formed from picture-element electrodes arranged in a matrix, counter electrodes facing the picture-element electrodes, and a liquid crystal layer interposed therebetween. The display state of each of the plurality of picture elements is controlled by an electric signal supplied thereto through a corresponding TFT connected to a corresponding scanning line and signal line.
A substrate of the TFT LCD on which the TFTs are formed (hereinafter, referred to as xe2x80x9cTFT substratexe2x80x9d) is made by repeatedly conducting the steps of depositing a semiconductor film, insulating film and conductor film on an insulating substrate and patterning these films. This necessarily results in production of defective TFTs that do not have normal TFT properties, short-circuit and disconnection of scanning line and signal line, and the like. The LCD fabricated with such a defective TFT substrate has defective picture elements (picture-element defects) that cannot provide prescribed display due to their failure to receive a normal voltage.
In particular, if a scanning line and a signal line of a normally white mode LCD are short-circuited at their intersection, a bright line 22 is produced on a liquid crystal panel 20, which extends crosswise along the scanning line and signal line from the short-circuited intersection 22a, as schematically shown in FIG. 8, thereby significantly degrading the display. Conventionally, such a display defect is repaired with, e.g., laser light. More specifically, the signal line is cut with laser light at positions interposing the short-circuited intersection 22a therebetween.
However, the inventor found that such a method for cutting a wiring with laser light has large variation in cutting accuracy and sometimes cannot completely cut the signal line when applied to, e.g., a signal line 3 of a multi-layer wiring structure having first and second conductive layers 3a and 3b as shown in FIG. 9.
The problems in repairing the defects of the conventional display devices have been described exemplarily for the TFT LCDs. However, these problems are not limited to the TFT LCDS, but are common to display devices having wirings of a multi-layer wiring structure (e.g., organic EL (electroluminescence) display devices).
The present invention is made to solve the aforementioned problems, and it is an object of the present invention to provide a display device capable of reliably and efficiently repairing defects, and a defect repairing method of the same.
According to the present invention, a display device includes a plurality of picture elements, a display state of each of the plurality of picture elements being controlled by an electric signal supplied thereto through a corresponding switching element connected to a corresponding scanning line and a corresponding signal line crossing the scanning line, wherein at least one of the scanning line and the signal line is a multi-layer wiring including first and second conductive layers, and the multi-layer wiring includes a low-stacked region where the second conductive layer is not formed. Thus, the aforementioned object is achieved.
The at least one of the scanning line and the signal line, which is a multi-layer wiring, may include the low-stacked region on both sides of an intersection with the other line.
The first conductive layer is preferably formed from a material having a smaller specific resistance value than that of the second conductive layer.
A width of an optimal laser power band for cutting the first conductive layer is preferably larger than that of an optimal laser power band for cutting the second conductive layer.
The display device may be a liquid crystal display device in which the plurality of picture elements include a liquid crystal layer.
According to the present invention, a method for repairing a defect in a display device including the aforementioned structure includes the step of cutting the first conductive layer by selectively radiating laser light to the first conductive layer formed in the low-stacked region. Thus, the aforementioned object is achieved.
Hereinafter, functions of the present invention will be described.
The multi-layer wiring having the first and second conductive layers has the low-stacked region where the second conductive layer is not formed. Accordingly, by radiating laser light to the low-stacked region of the multi-layer wiring, the first conductive layer (multi-layer wiring) can be reliably and efficiently cut without being affected by the second conductive layer. For example, the low-stacked region can be formed with a mask of a predetermined pattern that is prepared in the step of forming the second conductive layer. Therefore, no additional step is required to form the low-stacked region.
It should be appreciated that the multi-layer wiring may further have a third conductive layer in addition to the first and second conductive layers. In this case, it is preferable that the multi-layer wiring further has a region where the third conductive layer is not formed, and that this region is a low-stacked region where the second conductive layer is not formed. However, the present invention is not limited to this. As long as the multi-layer wiring has a low-stacked region where at least one conductive layer is not formed, the multi-layer wiring can be cut more reliably and efficiently by radiating laser light to that region than by radiating to another region. The second conductive layer is preferably formed on the first conductive layer. However, the present invention is not limited to this. It is preferable to omit a conductive layer that is less likely to be cut with laser light. It should be appreciated that the multi-layer wiring may have a semiconductor layer and/or an insulating layer in addition to the plurality of conductive layers.
It is preferable that at least one of the scanning line and the signal line, which is a multi-layer wiring, has a low-stacked region formed on both sides of the intersection with the other line. For example, in the case where the signal line is the multi-layer wiring, it is preferable that the signal line has a low-stacked region formed on both sides of the intersection with the scanning line, i.e., at positions interposing the intersection with the scanning line therebetween.
In the case where the first conductive layer is formed from a material having a smaller specific resistance value than that of the second conductive layer, the multi-layer wiring having low electrical resistance is easily realized, whereby a display device having excellent electrical properties is obtained.
When the width of the optimal laser power band for cutting the first conductive layer is larger than that of the optimal laser power band for cutting the second conductive layer, cutting of the low-stacked region is facilitated.